Complement activation and stimulation of chemotaxis by Chlamydia trachomatis.

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Acute chlamydial infection involves polymorphonuclear leukocyte (PMN) migration.
• The specific chemoattractants responsible for PMN recruitment in chlamydial infections are not fully understood.

Purpose of the Study:

• To investigate the in vitro chemotaxigenic effect of Chlamydia trachomatis elementary bodies (EB) on human plasma.
• To determine if complement activation is involved in the chemotactic response to C. trachomatis EB.

Main Methods:

• An agarose plate assay was used to measure PMN chemotaxis.
• Plasma from healthy donors, lacking anti-C. trachomatis antibodies, was incubated with L2 or DE strains of C. trachomatis EB.
• Complement activation was assessed by measuring C5a des-arginine levels via radioimmunoassay.

Main Results:

• Preincubation of plasma with L2 or DE C. trachomatis EB significantly enhanced PMN chemotaxis compared to plasma alone or EB in phosphate-buffered saline (PBS).
• Heat-inactivated plasma did not support EB-induced chemotaxis, indicating a heat-labile factor is involved.
• High levels of C5a des-arginine were detected in plasma incubated with EB, but not in plasma alone, heat-inactivated plasma, or EB in PBS.

Conclusions:

• L2 and DE strains of C. trachomatis EB possess chemotaxigenic properties for normal human plasma.
• The chemotactic effect is mediated, at least in part, by complement activation and the generation of C5a.
• These findings elucidate a key mechanism of innate immune cell recruitment during early chlamydial infections.